Heart rate monitors and other biometric sensors adapted for use with exercise equipment are becoming more prevalent. When the heart or other muscles contract, the body generates a very low amplitude electrical signal known as a biopotential signal. Biopotential signals can be electrically detected on the surface of a person's skin. Because the heart expands and contracts in a rhythmic manner, it generates a periodic biopotential signal which can be detected by a biometric sensor placed in contact with a person's skin.
Generally, heart rate monitors use electrodes to sense voltage fluctuations on a person's skin. The sensed signal is amplified and then filtered to identify the signal correlating to the heart rate. However, the use of high impedance, high gain amplifiers to measure differences in small electrical potentials can be complicated by unwanted electrical signals or noise if that noise is not present on both inputs to the amplifier. Since amplifiers do a good job of attenuating signals in common to both inputs, the difference does not contain the common noise. This is referred to as common-mode noise rejection.
A problem occurs when inputs to the amplifier senses voltage potentials that are physically separated from each other such that noise sources are picked up independently. In other words, the unwanted electrical signals are no longer common to the inputs of the amplifier. These non common-mode noise signals appear in the amplified signal and interfere with the signal of interest. This problem occurs in some types of exercise equipment. Therefore, it is desirable to provide a noise cancellation technique which may be employed with biometric sensors associated with such exercise equipment.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.